S6901 Open Ball Bearing Premium ABEC-5 Quality with Si3N4 Ceramic Balls (Silicon Nitride) 12mm x 24mm x 6mm S6901 Open Stainless Steel, radial and deep groove ball bearing,bearing is made of Stainless Steel with Ceramic Balls (Si3N4) and Stainless steel cage,the quality is set to EMQ (Premium ABEC-5 quality) to ensure high speed, inner diameter is 12mm, outer diameter is 24mm and width is 6mm.